If you plan to do it on openwrt I would make sure before you buy. Especially if you’re trying to save on the mesh nodes and not buy a fully outfitted router for each node.

If you’re going to dive in to openwrt from google wifi you should probably start with ready made hardware.

https://forum.openwrt.org/t/best-newcomer-routers-2024/189050

Please keep in mind that to duplicate mesh functionality it’s going to take a significant effort and you need to make sure the hardware you buy is compatible with 802.11s. Open WRT forums have hardware compatibility rundowns of known working routers so it’s not too difficult to find them.

This is a much bigger uphill battle rolling your own hardware unless you just plan to buy a separate access point or two for hardware and skip the mesh functionality.